Apparatus for making regenerated cellulose film



Feb. 16, 1960 H. E. RoscoE 2,925,083

APPARATUS FOR MAKING REGENERATED CELLULOSE FILM Filed June 23. 1958 HOWARD EARL ROSCOE ATTORNEY INVENTOR United States Patent O APPARATUS FOR MAKING REGENERATED CELLULOSE FILM Howard Earl Roscoe, Lawrence, Kans., assigner to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Application June 23, 1958, Serial No. 743,568

3 Claims. (Cl. 134-64) This invention relates to the manufacture of continuous webs of regenerated cellulose film from viscose solutions. More particularly, it relates to improvements in the guiding and handling of sheet material through the casting machine whereby regenerated cellulose film having improved transparency, durability, -and surface characteristics is obtained.

The present invention is an improvement inthe current method of manufacturing regenerated cellulose film in a continuous manner from viscose as disclosed in U.S. Patent No. 1,548,864 to Brandenberger. This general procedure, which is particularly well suited to a commercial scale operation, involves continuous extrusion of a sheet of cellulose xanthate solution (viscose) through a narrow slot directly in to an acid-sulfate coagulating and/or regenerating bath, where it is kept until it has acquired the mechanical strength necessary to withstand the subsequent treatments which it receives in the subsequent sections of the casting machine.

After the web has become strong enough, it is removed from the coagulating and/or regenerating bath and passed through a liquid bath, usually a dilute acid bath, wherein regeneration of the cellulose xanthate to cellulose is completed. After leaving this bath, the web is subjected to a series of washing, desulfuring and bleaching (or dyeing, depending upon the use which is to be made of the product) treatments. These last mentioned treatments, like the coagulating and regenerating steps, are conveniently carried out by passing the continuous web through vats containing the corresponding treating liquids; water for washing, a hot dilute aqueous solution of caustic soda or sodium sulphide or both for desulfuring and an aqueous solution of sodium or calcium 1 .A` for bleacing. After the cellulose wel; leaves the last washing bat and before it is dried, it is customary to provide a softening step wherein the cellulose web is passed through an aqueous solution of glycerol or ethylene glycol. As a final step in the manufacture, the cellulosic sheet material is dried (usually by passing it over heated rolls) and collected in mill rolls for storage, transportation, etc.

In transporting the cellulosic web through the baths in the aforementioned procedure, a very serious problem has been encountered. The upper rotating rolls which are exposed to the atmosphere, are subject to extreme corrosion from the combination of the oxygen in the air and the chemicals in the various treating solutions. The rubber covering used over these rolls tends to become dimensionally unstable after a relatively short period of time. This dimensional instability imparts distortions and undesirable surface characteristics on the regenerated cellulose film passing thereover.

The object of the present invention is to provide upper rotating roll surfaces which avoid the above diliiculties. More specifically, the object is to provide upper rolls which remain dimensionally stable over extended periods of time. Other objects will appear hereinafter.

The objects are accomplished by a rotatable roll com- Patented Feb. 16, 1960 ICC prising a cylindrical metal body, preferably steel; a rubber covering over said body and polyvinyl chloride tubing, preferably aged and having the physical properties given below, disposed over said rubber covering. Such a roll, when installed over a bleaching tank containing an aqueous solution of sodium hypochlorite at room temperature (which represents the severest conditions encountered in regenerated cellulose film treatment), outlasted previously used rolls more than three-fold.

The physical properties of the tubing disposed over the rubber covering should fall within the following ranges:

Shore D Durometer Hardness 82-86 (ASTM D-785). Specific gravity 1.3-1.5 (ASTM D-792). Tensile strength (p.s.i.

at 78 F.) 6,400-7,000 (ASTM D-638). Comprcssive strength (p.s.i. at 78 F.) 9,000-10,000 (ASTM D-695). Flexural strength (p.s.i.

at 78 F.) l3,000-14,000 (ASTM D790).

The invention will be more apparent by referring to the following description when read in conjunction with the drawings, in which:

Figure 1 is a side elevation of the wet end tanks employed in the production of regenerated cellulose film;

Figure 2 is an illustration in perspective of an upper rotating guide member of the present invention mounted over a tank; and

Figure 3 is a sectional view of the guide member along line 3 3 of Figure 2.

Referring to Figure l, the various treating tanks are indicated by the numerals 1-15. These tanks are conventional and are described in U.S. Patent No. 1,548,864. After leaving tank 15, the lm is usually passed over drying rolls (not shown) prior to being wound into mill rolls. Numeral 16 represents the gel film. The positively driven upper guide rolls are shown at 18 and the stationary lower guide members are indicated by 17.

In Figure 2, the continuous web of gel regenerated cellulose film is passed over the roll 18, the roll mounted in suitable brackets, one of which is shown at 19, and driven by a motor (not shown). This roll guides the web down into the treating tank 15 where it passes around the lower guide roll 17. The upper guide roll 18 as shown in Figure 3, is composed of a cylindrical steel body 20, a rubber covering 21 over the steel body and polyvinyl chloride tubing 22 over the rubber covering. Discs 23 of polyvinyl chloride are liquid-welded to the polyvinyl chloride tubing 1S at the ends of the roll by means of a solvent cement. Sections of rigid polyvinyl chloride pipe 24 are pushed over the rubber covered sections of the roll shaft 25 into abutment with the polyvinyl chloride discs and are then liquid-welded to the discs.

In preparing the roll, the hard rubber covering on the steel roll body is first machined to an interference fit of 0.010 inch with respect to the inside diameter of the polyvinyl chloride tube. Polyvinyl chloride known as type I or normal impact grade in the trade is extruded through a die, the die having an outside diameter of 5 .0001-0025 inches and a thickness of 0.250i0-010 inch, to produce the polyvinyl chloride tubing. The polyvinyl chloride tubing is then pushed over the rubber covered steel roll body and an initial machining operation performed, in which the polyvinyl chloride cover is turned to an oversize diameter. The roll is then allowed to age for 5 days to permit the polyvinyl chloride tubing and the rubber covering to achieve a permanent configuration. Finish machining is then performed to reduce the diameter to a tolerance of 4.915 inchesiOOZ. Thereafter, the discs 23 and the pipe sections 24, also of type I polyvinyl chloride, are fitted into place.

Having fully disclosed the invention, what is claimed 1s:

l. In an apparatus for treating gel regenerated cellulose tilm comprising a tank containing a treating liquid, upper and lower guide members, the upper guide members being positively driven rolls and the lower guide members being stationary members, the upper guide members being above the treating liquid and the lower guide members being immersed in the liquid, the upper and lower guide members being arranged to guide the regenerated cellulose lm in a circuitous pattern through the treating liquid, improved upper guide members comprising a cylindrical metal body, a rubber covering over said metal body, and polyvinyl chloride tubing disposed over said rubber covering, said polyvinyl-chloride tubing having a hardness of 82-86, a specific gravity of l.3l.5, a tensile strength of 6,400-7,000 p.s.i., a compressive strength of 9,000-10,000 p.s.i. and avflexural strength of 13,000-14,000 p.s.i., said strengths measured at a temperature of 78 F.

2. In an apparatus for treating gel regenerated cellulose film comprising a tank containing a treating liquid, upper and lower guide members, the upper guide members being positively driven rolls and the lower guide members being stationary members, the upper guide members being above the treating liquid and the lower guide members being immersed in the liquid, the upper and lower guide members being arranged to guide the regenerated cellulose lm` in a circuitous pattern through the treating liquid, improved upper guide members comprising a cylindrical steel body, a rubber covering over said steel body, and polyvinyl chloride tubing disposed over said rubber covering, said polyvinyl chloride tubing having a hardness of 82-86, a specic gravity of 1.3-1.5, a tensile strength of 6,400-7,000 p.s.i., a compressive strength of 9,000-10,000 p.s.i. and a ilexural strength of 13,00014,000 p.s.i., said strengths measured at a temperature of 78 F.

3. In an apparatus for treating gel regenerated cellulose lm comprising a tank containing a treating liquid, upper and lower guide members, the upper guide members being above the treating liquid and the lower guide members being immersed in the liquid, the upper and lower guide members being arranged to guide the regenerated cellulose lm in a circuitous pattern through the treating liquid, improved upper guide members comprising a cylindrical metal body, a rubber covering over said metal body, and polyvinyl chloride tubing disposed over said rubber covering, said polyvinyl chloride tubing having a hardness of 82-86, a specific gravity of 1.3-1.5, a tensile strength of 6,400-7,000 p.s.i., a compressive strength of 9,000-10,000 p.s.i. and a flexural strength of 13,000-14,000 p.s.i., said strengths measured at a temperature of 78 F.

References Cited in the flle of this patent UNITED STATES PATENTS 2,312,853 Toland Mar. 2, 1943 2,631,358 Hill Mar. 17, 1953 2,650,603 Howes Sept. 1, 1953 

1. IN AN APPARATUS FOR TREATING GEL REGENERATED CELLULOSE FILM COMPRISING A TANK CONTAINING A TREATING LIQUID, UPPER AND LOWER GUIDE MEMBERS, THE UPPER GUIDE MEMBERS BEING POSITIVELY DRIVEN ROLLS AND THE LOWER GUIDE MEMBERS BEING STATIONARY MEMBERS, THE UPPER GUIDE MEMBERS BEING ABOVE THE TREATING LIQUID AND THE LOWER GUIDE MEMBERS BEING IMMERSED IN THE LIQUID, THE UPPER AND LOWER GUIDE MEMBERS BEING ARRANGED TO GUIDE THE REGENERATED CELLULOSE FILM IN A CIRCUITOUS PATTERN THROUGH THE TREATING LIQUID, IMPROVED UPPER GUIDE MEMBERS COMPRISING A CYLINDRICAL METAL BODY, A UBBER COVERING OVER SAID METAL BODY, AND POLYVINYL CHLORIDE TUBING DISPOSED OVER SAID RUBBER COVERING, SAID POLYVINYL CHLORIDE TUBING HAVING A HARDNESS OF 82-86, A SPECIFIC GRAVITY OF 1.3-1.5, A TENSILE STRENGTH OF 6,400-7,000 P.S.I., A COMPRESSIVE STRENGTH OF 9,000-10,000 P.S.I. AND A FLEXURAL STRENGTH OF 13,000-14,000 P.S.I., SAID STRENGTHS MEASURED AT A TEMPERATURE OF 78*F. 